This laboratory will continue to utilize three amphibian model systems, the American common newt, Notophthalmus viridescens, the South African Clawed tad, Xenopus laevis, and the common American Grass frog, Rana pipiens, which provide both an evolutionary and immunologic progression. Moreover, the emphasis will continue to focus on regulatory mechanisms which affect humoral immunity. In particular, great depth of understanding at the mechanistic level will be sought for such phenomena as carrier specific amplification and suppression of anti-hapten responses. Antigen competition and hapten specific tolerance is also being explored. Additionally, the regulatory capacities of phagocytes, metamorphic effects and carrier dependence of hapten specific subsets of responding cells will receive continued attention. The phenomenology of all of the above has been part of the ongoing program here for the past five years. During the near future, a new area of investigation on the genetics of the evolution immunoglobulin diversity will also be added.